1. Field of the Invention
The present invention relates to a heat sink configured to be fitted to a memory module, and a memory module fitted with a heat sink, and more specifically to a heat sink configured to be fitted to a memory module composed of a plurality of DRAMs mainly mounted on a printed circuit board, and such a memory module fitted with a heat sink.
2. Description of Related Art
Recently, an increase of the operation speed and the storage capacity in semiconductor memories such as a DRAM (dynamic random access memory) is being rapidly advanced. With an increased integration density of the semiconductor memories, a generated heat amount of the semiconductor memory ICs (integrated circuit) increases correspondingly. In addition, the down-sizing of a module accommodating microelectronic components including the semiconductor memory ICs is demanded. On the other hand, it is in some cases that a memory module includes an IC or the like for compensating for a time delay of a signal caused by an increased operation speed of individual DRAMs. As a result, many ICs and chip-type circuit components are mounted on a printed circuit board in addition to the semiconductor memory ICs, so that the number of components mounted in a memory module has a tendency to increase.
Now, a prior art memory module will be described with reference to FIGS. 1A and 1B, which are a diagrammatic plan view and a diagrammatic side view of one typical example of the prior art memory module. As shown in FIGS. 1A and 1B, the memory module is generally designated with reference number 10, and includes a number of packaged memory ICs 3 and a plurality of chip-type capacitors 2 mounted on each face of a printed circuit board 1. The printed circuit board 1 has an array of contact pads 4 provided along a long-side edge of each face of the printed circuit board 1 for electrical connection with an appropriate mating socket.
As seen from FIGS. 1A and 1B, the semiconductor memory ICs 3 and the chip-type capacitors 2 are mounted on each face of the printed circuit board 1 in a naked condition, and the memory module 10 is inserted into a slot within a system such a personal computer in this naked condition. Therefore, heat generated in the memory ICs 3 is radiated from only the surface of the memory ICs 3.
In the prior art memory module as mentioned above, since the heat radiation from the surface of the memory ICs is only the dissipation of the heat generated in the memory ICs, a satisfactory heat dissipation efficiency cannot be obtained. Further, since the heat radiating efficiency itself is influenced by a shape of the DRAM package, a new problem is encountered in that the performance of the memory drops because of an increased heat of the DRAM caused with an increased integration density.
In addition, since the prior art memory module is assembled in the condition that all components mounted on the module are in a naked condition, there is high possibility that the chip-type components such as capacitors and resistors located at a peripheral zone of the printed circuit board of the memory module are broken or lost because of a mechanical shock in the course of transportation. Furthermore, with an increased performance of the ICs mounted on the printed circuit board of the memory module, a pin pitch of the packaged ICs becomes narrow, with the result that there occurs another new problem such as a short-circuiting between the pins of the IC caused by an external cause.
Besides, the components including the memory ICs are ordinarily mounted on the printed circuit board by locating the components on a solder paste printed on the printed circuit board, and putting the printed circuit board into a reflow oven so that the components are soldered on the printed circuit board. In this process, the printed circuit board is often warped, and if the components are mounted on the warped printed circuit board, when the memory module is inserted into a slot within a system such as a personal computer, a stress acts on the printed circuit board, with the result that the components are peeled off from the printed circuit board.
Japanese Patent Application Pre-examination Publication No. JP-A-07-202120 (an English abstract of JP-A-07-202120 is available and the content of the English abstract is incorporated by reference in its entirety into this application) proposes a high heat radiating memory constructed to efficiently radiate heat generated from a memory IC, by bonding the packaged memory IC to one surface of a heat radiating substrate and by covering the packaged memory IC and the one surface of the heat radiating substrate with resin.
This prior art is intended to elevate the heat radiating efficiency of individual memory ICs, with the result that the memory module composed of a number of memory ICs having a high heat radiating efficiency mounted on a printed circuit board, can have a high heat radiating efficiency in total. However, the individual memory IC becomes complicated in structure and expensive, and therefore, the memory module correspondingly becomes expensive. In addition, this approach cannot solve the problem of the warping of the printed circuit board.
Accordingly, it is an object of the present invention to provide a heat sink configured to be fitted to a memory module, and a memory module fitted with a heat sink, which have overcome the above mentioned problems of the prior art.
Another object of the present invention is to provide a heat sink which is configured to be fitted to a memory module, and which can efficiently dissipate heat generated from packaged semiconductor memories such as DRAMs mounted on the memory module, and can protect components mounted on a printed circuit board of the memory module, from a mechanical shock, and also can discriminate the degree of warping of the printed circuit board having the packaged semiconductor memories and the other components mounted thereon.
Still another object of the present invention is to provide a memory module fitted with the above mentioned heat sink.
The above and other objects of the present invention are achieved in accordance with the present invention by a heat sink configured to be fitted over a memory module composed of a plurality of packaged memory integrated circuits mounted on a printed circuit board, the heat sink having a U-shape in cross section so that the memory module can be inserted into a U-shaped recess of the heat sink with a thermal conductive material being interposed between the heat sink and the packaged memory integrated circuits mounted on the printed circuit board and being in contact with the heat sink and the packaged memory integrated circuits.
In one embodiment, the thermal conductive material is a high thermal conductive member, and the heat sink is formed of a resilient material to have a clip function so that the memory module is mechanically held by the heat sink through the high thermal conductive member. Preferably, the heat sink has a number of convexities on an outer surface thereof to having an increased outer surface area.
According to another aspect of the present invention, there is provided a memory module composed of a plurality of packaged memory integrated circuits mounted on a printed circuit board, and fitted with a heat sink having a U-shape in cross section in such a manner that the memory module is inserted into a U-shaped recess of the heat sink with a thermal conductive material being interposed between the heat sink and the packaged memory integrated circuits and being in contact with the heat sink and the packaged memory integrated circuits
In one embodiment, the thermal conductive material is a high thermal conductive member, and the heat sink is formed of a resilient material to have a clip function so that the memory module is mechanically held by the heat sink through the high thermal conductive member. Preferably, the thermal conductive member is a high thermal conductive rubber having an electrical insulative property, and the heat sink has a number of convexities on an outer surface thereof to having an increased outer surface area.
The heat sink can be detachable from the memory module. In another embodiment, the thermal conductive material is a silicone grease.
More preferably, the heat sink has a length of the heat sink and a depth of the U-shaped recess sufficient to cover all of the packaged memory integrated circuits mounted on a printed circuit board.
The above and other objects, features and advantages of the present invention will be apparent from the following description of preferred embodiments of the invention with reference to the accompanying drawings.